Plastic and its link to obesity: Information, Research, Causes, Symptoms and Treatment

They say diet and too little exercise clearly are key reasons for the worldwide rise in obesity in the past 20 years, but they may not be the only ones. Food intake and exercise just haven't changed that much in that period, they argue. And while genetics obviously play a role — just think of someone you know who can eat three Big Macs a day and never gain an ounce — these researchers say it would be impossible to see such widespread genetic change in just two decades, giving them more reason to suspect the environment.

"This is a really new area . . . but from multiple labs on multiple levels we are getting preliminary data that all say the same thing: Chemicals can play a role," said Jerry Heindel, a program administrator for the National Institute of Environmental Health Sciences. "We know that nutrition and exercise are very, very important, but underlying that could be environmental exposures during development that alter your physiology, including how you respond to food and exercise."

Thousands of chemicals have come on the market in the past 30 years, and some of them are showing up in people's bodies in low levels. Scientists studying obesity are focusing on endocrine disrupters — which have already been linked to reproductive problems in animals and humans — because they have become so common in the environment and are known to affect fat cells.

One key researcher in the field, Bruce Blumberg of the University of California, Irvine, has even coined a new word for chemicals that can make you fat: Obesogens.

A recent US Centers for Disease Control and Prevention study found that about 93 percent of the US population had bisphenol A, a chemical that can be found in canned goods and in hard, clear plastic items such as baby bottles and hiking containers, in their body. A study at the University of Missouri-Columbia showed that mice fed bisphenol A during early development — at lower amounts than what would have resulted in the levels found in most people in the CDC study — become markedly more obese as adults than those that weren't fed the chemical. Tufts University scientists observed similar phenomenon in rats.

The chemical industry, however, disputes those studies and says dozens of others that examined bisphenol A showed no weight gain.